The near-infrared region corresponds to an absorption spectrum range related to biological objects such as plants and animals, and the environment. Therefore, the development of a detector of near-infrared light, the detector including an absorption layer composed of a group III-V compound semiconductor, has been actively conducted. A known example of a detector that converts photo-induced charge into an output signal includes a light receiving element array in which the sensitivity is extended to a wavelength of 2.6 μm by using extended-InGaAs as an absorption layer and a complementary metal-oxide semiconductor (CMOS) functioning as a read-out IC (ROIC) and connected to the light receiving element array (NPL 1). In the light receiving element array, electrons of electron-hole pairs generated by incident light are collected in a common n-side electrode, and holes of the electron-hole pairs are read out from a p-side electrode, which is a pixel electrode, to the CMOS.
In addition, it has been reported that a pin-type photodiode including an absorption layer having a type-II multi-quantum well structure (MQW) composed of InGaAs/GaAsSb and a p-type pixel region has a sensitivity up to a wavelength of 2.5 μm (NPL 2). Furthermore, in order to obtain a satisfactory crystal quality of a type-II InGaAs/GaAsSb MQW that absorbs near-infrared light having a wavelength of up to 3 μm, a laminated structure of a photodiode and a method for producing the photodiode have been proposed (PTL 1).
It has also been reported that when the above type-II MQW composed of InGaAs/GaAsSb is grown without doping, the MQW has the n-conductivity type (NPL 3 and NPL 4). In such a case, the photodiode may be referred to as an n-type photodiode rather than a pin-type photodiode. In general, a photodiode obtained in this case is also included in the category of pin-type photodiodes. The above pin-type photodiode can be obtained by easily forming a p-type region in each light receiving element using Zn, which is a p-type impurity and for which abundant data has been accumulated.